The present invention relates to an electrode for an electronic source, a method for producing the same, and an electronic tube using the same.
Known electrode tubes include a fluorescent display tube in which electrons emitted from an electron source disposed at a side of a cathode electrode are collided with a light emitting part comprising a fluorescent layer formed on a counter electrode to emit light. The electron tube is one of vacuum micro devices using sub-micron to micron order of micro electron emitting sources. A basic structure of the electron tube is a triode similar to that of a conventional vacuum tube. However, the electron tube does not use a hot cathode electrode, but uses an electron emitting source as the electrode. In the electron emitting source, a cathode electrode (emitter) is applied high electric field to draw electron through the quantum mechanics tunnel effect.
The drawn electrons are accelerated by a voltage between anode and cathode electrodes, and are collided and excited with the fluorescent layer formed on the anode electrode to emit light. It utilizes the same principle as that of a cathode ray tube in that a phosphor is excited by a cathode ray to emit light. The electron tube is advantageous over the cathode ray tube because the electron tube has decreased volume, weight, and electric power consumption. In addition, a device utilizing the electronic tube does not require a back light, and has a wide visual field as compared to a liquid crystal display device.
FIGS. 6 and 7 show one example of the electrode for the electron source. FIG. 6 is a view showing structures of a cathode electrode and an electron drawing electrode. FIG. 7 is a view showing a structure of an electron tube comprising an anode electrode as well as the cathode and electron drawing electrodes.
An electrode for the electron source 6 used as the cathode electrode comprises a conductive substrate 7, an electron emitting source 8 such as carbon nanotube, and diamond-like carbon formed on a surface of the substrate 7. An electronic drawing electrode 9 having a mesh part 9a formed in a lattice is disposed substantially parallel to the electron emitting source 8.
In such a structure, a voltage is applied such that the electron drawing electrode 9 has positive potential against the electrode for the electronic source 6, which induces field electrons emission. Thus, the electrons are drawn from the electrode for the electronic source 6. Some drawn electrons flow into the electron drawing electrode 9, and others pass through the mesh part 9a and flow into an anode electrode 10 as shown in FIG. 7.
However, in the electrode structures shown in FIGS. 6 and 7, the numbers of the electrons flowing into the electron drawing electrode 9 are greater than that of the electrons passing through the electron drawing electrode 9 so that the phosphor makes light emission. The percentage of anode current IA in the total current is low. The total current is grid current IG plus the anode current IA, and the percentage is hereinafter referred to as a “current distribution percentage”. The potential of the electron drawing electrode 9 is distributed parallel to the electrode for the electronic source 6 used as the cathode electrode. Accordingly, the numbers of electrons eG− emitted from the electrode for the electronic source 6 to the electron drawing electrode 9 are greater than those to the anode electrode 10 through the mesh part 9a, as shown by arrows in FIG. 6. As a result, the percentage of the grid current IG that does not contribute to light emission becomes high. It could be considered that the electrons, emitted from the electrode for the electronic source 6 not disposed directly beneath the mesh part 9, generate the grid current that less contributes to the light emission, i.e., wattless current. Through the studies of the present inventor, the conventional electrode structure could provide the current distribution percentage of 5 to 10%. When a space between the electron drawing electrode and the electrode for the electron source is narrow, they may be undesirably contacted each other.
Generally, the electron emitting source is formed on the surface of the flat solid conductive substrate. Alternatively, the conductive substrate may have a plurality of holed on its surface. When the electron emitting source is formed on such a substrate with holes by a dry method such as a CVD method, the electron emitting source such as carbon nanotube is formed not only on a front surface of the substrate, but also on a rear surface of the substrate through the holes. The electron emitting source formed on the rear surface opposite to the surface from which the electrons are emitted is not easily removed by a blower. Therefore, there is the following problems.    (1) When the conductive substrate on which the electron emitting source is formed is fixed to other base metal, the electron emitting source is caught between the conductive substrate and the base metal, whereby it is difficult to form the flat electrode, and repeatability of a gap between the electron drawing electrode and the electrode for the electronic source becomes poor.    (2) Since the conductive substrate is welded to the base metal via the electron emitting source such as the carbon nanotube, welding strength is decreased.    (3) The electron emitting source enters into the space between the electron drawing electrode and the electrode for the electron source when the electrode is assembled, thereby causing a contact problem.